Transformers worksheet with answers

Free printable Transformers worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

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1.Easy

An ideal transformer has 100 turns on its primary winding and 2500 turns on its secondary winding. The primary is connected to a 230 V AC supply. Find the secondary voltage V₂.

N₁ = 100N₂ = 2500V₁ = 230 V

V₂ = V

2.Easy

An ideal transformer must step 920 V down to 230 V. Its primary winding has 80 turns. How many turns N₂ does the secondary winding need?

V₁ = 920 VV₂ = 230 VN₁ = 80

N₂ =

3.Medium

A single-phase 100 kVA, 11000/400 V transformer operates at its rated load. Treat it as ideal. Find the current I_LV in the low-voltage winding.

S = 100 kVAV₁ = 11000 VV₂ = 400 V

I_LV = A

4.Medium

An ideal transformer with a turns ratio N₁:N₂ = 2:1 has 240 V applied to its primary winding. An 8 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 2:1V₁ = 240 VR_L = 8 Ω

I₁ = A

5.Hard

A single-phase 75 kVA transformer has a core loss of 300 W and a copper loss of 600 W at rated load. It supplies 25% of its rated kVA at a power factor of 0.9 lagging. Find the total losses P_loss in watts at this load.

S = 75 kVAP_core = 300 WP_cu,fl = 600 Wx = 0.25pf = 0.9

P_loss = W

6.Hard

A single-phase 150 kVA transformer has a core loss of 750 W and a copper loss of 2250 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 150 kVAP_core = 750 WP_cu,fl = 2250 W

S_η,max = kVA

Answer key

1. V₂ = 5750 V
2. N₂ = 20
3. I_LV = 250 A
4. I₁ = 7.5 A
5. P_loss = 337.5 W
6. S_η,max = 86.6 kVA

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